Babies are born with the instinct to suckle milk from their mothers' breasts, but it is often necessary for them to drink liquids from other sources. Babies are unable to drink liquids from glasses or cups without spilling so it is common throughout the world to feed liquids to babies in nursing bottles, also known as baby bottles. A nursing bottle features a rubber nipple with a small hole in its tip secured across an opening in the top of a liquid container. A nursing bottle is used by filling the container with liquid, securing the nipple, inverting the bottle, and placing the nipple into the baby's mouth. The baby then sucks on the nipple to withdraw the liquid. Unfortunately, the use of a nursing bottle can cause tooth decay, also known as dental caries.
Tooth decay is the erosion of the protective enamel surface of the tooth which occurs when the tooth is exposed to an acidic environment. The human mouth contains various types of bacteria, including Streptococcus mutans. S. mutans digest simple carbohydrates such as sucrose (table sugar) and produce acidic wastes. When a simple carbohydrate is introduced into the mouth, S. mutans multiply and their acidic wastes can drastically affect the acidity of the mouth. While the normal pH in the mouth is about 7 (neutral), the pH can drop to about 4 when a concentrated sucrose solution is consumed. Tooth enamel softens and erodes when exposed to a pH less than about 6.5. It can thus be seen that foods and liquids containing simple carbohydrates do not directly cause tooth decay. Instead, they cause a multiplication of S. mutans, whose acidic wastes are responsible for the erosion of the tooth enamel. Foods and liquids that contain simple carbohydrates and lead to tooth decay are referred to as cariogenic. Common cariogenic liquids include milk, fruit juices, and sugar-sweetened carbonated sodas.
The amount of tooth enamel erosion that occurs when a cariogenic liquid is consumed is a function of both the acidity in the mouth and the duration of the acidic conditions. These two factors are, in turn, dependent upon the concentration of simple carbohydrates in the liquid, the duration the liquid is in the mouth, and whether the liquid is rinsed or diluted by saliva, water, or other non-cariogenic liquid. When an adult drinks a cariogenic liquid from a glass or bottle, natural swallowing and saliva production help to rinse the cariogenic liquid off the teeth. However, this type of beneficial rinsing is sometimes absent when a baby drinks milk, formula, fruit juice, or other cariogenic liquid from a nursing bottle. When babies drink from a nursing bottle, they tend to fall asleep with the nipple still in their mouths. Both saliva production and swallowing slow or stop during sleep. Accordingly, the conditions in the sleeping baby's mouth are ideal for tooth decay--a cariogenic liquid rich in sugar is present for a long period of time and there is no rinsing of the cariogenic liquid from the teeth. Babies whose care-providers allow them to routinely fall asleep with nursing bottles in their mouths develop tooth decay at a horrifying rate.
Tooth decay from the use of nursing bottles can be reduced by ensuring that babies do not fall asleep while nursing. Unfortunately, this type of tooth decay continues, especially among lower socioeconomic groups, despite extensive efforts in warning of the dangers. See, e.g., Claudia Benitez et al., "Effect of a preventive approach for the treatment of nursing bottle caries," Journal of Dentistry for Children, January-February 1994, at 46. It would be very desirable to provide a nursing bottle that reduced this type of tooth decay even if the baby is allowed to fall asleep with the bottle in the mouth.
Lake, U.S. Pat. No. 4,971,211, issued Nov. 20, 1990, discloses a nursing bottle having two reservoirs and two nipples so one of two liquids can be selectively dispensed. There is no mechanism for simultaneously dispensing both liquids and, if the baby falls asleep while drinking a cariogenic liquid, the same problems of tooth decay occur as with a conventional nursing bottle. Accordingly, a demand still exists for a nursing bottle that reduces tooth decay.